GB2522930A

GB2522930A - A heater apparatus

Info

Publication number: GB2522930A
Application number: GB1402357.6A
Authority: GB
Inventors: Richard Harpum
Original assignee: LIMPET HEATING Co Ltd
Current assignee: LIMPET HEATING Co Ltd
Priority date: 2014-02-11
Filing date: 2014-02-11
Publication date: 2015-08-12
Anticipated expiration: 2034-02-11
Also published as: GB2522930B; GB201402357D0

Abstract

A heater 10 attaches to a work piece or field device 110 for heating thereof. It has a source of heat (74, fig 3), at least one sensor, a controller (70, fig 3) for controlling the heater 10, a communication port (30, fig 3), and attachment means for attaching an adapter block. A replaceable pre-selected shaped adapter block 120 attached to the heater 10 via the attachment means. The shape is selected for intimate contact with the work piece 110. The adapter block transfers heat from the source of heat to the work piece 110 by direct conduction. There may be a number of interconnected heaters 10 in a master and slave arrangement (fig 6).

Description

A heater apparatus The present invention relates generally to a heater apparatus, a heater system, and a method of heating of work pieces, and finds particular, although not exclusive, S utility in industrial applications It is often important to heat machinery and other infrastructure within industrial processes to maintain an efficient operation. One simple example is that of frost protecion of pipe-work, but equally applicable is process heating.

Ihe invention serves to address the difficulty in heating compact areas of bulky metal work pieces that often have complex body profiles (e.g., pumps, valves, flanges, meters, plates, etc., but not restricted to these) that generally only expensive water systems can heat effectively (although inefficiently). The present alternative electrical offerings are trace heat cable or bespoke wired heating systems with external controllers.

Whilst trace heating provides a low cost solution, for these type of work piece applications the result is often very poor and gcnerally unreliable at heating, together with an increased risk of electrocution of users. Bespoke electrical heating systems, whilst producing effective results, become expensive to install and need a relatively high degree of expertise to desigp and install Present centralised control systems are known \vhich comprise heaters, separate temperature sensors, a central control cabinet and cabling, the cabling connects the sensors to the cabinet; it also supplies power to all the heaters. Finally, cabling is used to provide control to the heaters based on the sensors output and the control settings.

the cabinet includes a multitude of individual control systems and/or a PLC, Other de-centralised ("distributed input/output" or Ccnetrvorkecl input/output") systems are known which reduce the amount of cabling. This is because instead of having cabling going to each individual heater and sensor, localised controllers are located near the heaters and sensors, This allows for the power and signalling to be grouped together and then transmitted back to the central control system. This is often effected by use of a singe power cable and a sinØe communications cable to alocalised controller from which cables were then used tc connect to the heaters and sensors, For situations where a niultitude of heaters, \vhich all need individual control loops are required. the system is relatively expensive. Every heater and sensor requires a supply of power, a network or traditional route for sensor connection, a multitude of

I

individual controllet-s or a mass of control ioops written in software, and an appropriate touch screen in interfiicc with and regulate set the temperature set points.

It is desirable, thetefore, to provide apparatus which reduces sri11 ftirthet-the amount of cabling and other infrastructure.

S In a first aspect, the invention provides a heater apparatus br attachment to an external work piece for hearing thereof the apparatus comprising a source of hear, at least one sensor, a controller for controlling the apparatus, at least one communication port, attachment means for attaching an adapter block, and a replaceable pt-c-selected shaped adapter block attached to the apparatus via the attachment means, the shape selected for intimate contact with die external work piece, the adapter block for transferring heat from the source of heat to the external object by direct conduction.

In this manner, the controller is arranged integrally with the apparatus rather than being separate. A desired temperature value may he set by the user and the apparatus may operate to maintain that temperature as measured by a temperature sensor.

the adapter block may he configured to store heat as well as transfer heat. the heat 1-nay flow froni the adapter block via conduction at a rate of approximately 200 W/mK. l-Iigher and/or lower rates are contemplated. lime adapter block rna be attachable to the heater apparatus by the use of screws, bolts or other such means. Heat transfer tape (which may he adhesive) may he arranged between the adapter block and the apparatus, and/or between the adapter block and the work piece.

Tbe work piece may be any of a pipe, a pump, a valve, a meter. an engine, a flange, vessels, and other such infrastructure. the apparatus is primarily ainied at industrial use, rather than domestic use, althougiim domestic use is a possibility. The source of heat may he an electrically powered heater. The sensor [nay he a temperature sensor arranged within the apparatus.

The controller may be arranged to control the temperature of the heat source and may control the ramp-rate of the source of heat. In this manner the rate at which heat is created by the heat source, and/or the rate of change of its temperature, may he controllable.

The apparatus may include temperature pre-set means for pre-setting the maximum temperature at which the heat source is to operate.

The controller may be a lict-oprocessot-. Potting compound may be used to prctect the electromc coniponents froni water and/or vibration, The controller may bc attached to the source of heat within the apparatus. The controller may be a PCIB. The controller may be located on top of the heat source opposite from the adapter plate S when fitted.

The controller may be arranged to communicate, via die at least one communication port, actively and/or passively with a remote device so that the status of the apparatus may be determined from the remote device, AS-I may be used as the conununic ation fhrinat, although other thrinats are contemplated.

An example of a remote device is a computer or PLC, The remote device requires no connrol loops or discrete controllers. The status may be any one or more of power consumption kW), on/off state. temperature, the pre-set maximum/operating temperature, the presence or absence of a problem as pre-defined and as monitored by the controller, and other such aspects.

Ihe apparatus may he antonomous, Ihe controller may be arranged to communicate, via die at least one commununication port, actively and/or passively with a remote device so that the apparatus may be operated from die reniote device. In tIns regard, die term "operated" may mean that the settings are adjustable via the remote device. In this regard, a PWDvI signal may he used to control the temperature of the source of heat.

Ihe controller may he arranged to control at least one other heater apparatus via the at least one communication port. The port may he the same or a difterent port from xvhich the apparatus communicates xvith the remote device, I'he apparatus may he deemed a "master" unit and the at least one other apparatus a "slave" unit, The controller in the master unit (flay control the slave unit in the same manner in which it operates the master unit, The master unit may be arranged such that more than one slave unit may be connectable to it.

The slave unit (flay not include a controller, instead relying on the controller in the master unit, A connected array of master and/or slave units niay be created to prcduce a temperature gradient on a work piece.

The controller may he arranged to communicate, via the at least one cominumcation pcrt, actively and/or passively with a remote device so that the status of the at least one other-heater apparatus may be determined from the remote device.

likewise, the controller may be arranged to communicate, via the at least one S cominumcation port, actively and/or passively with a remote device so that thc operation of the at least one other hearer apparatus may be controlled from the remote device.

The port may be the same or a different port from which the apparatus communicates with the remcte device, the control of the at least one other (slave) apparatus may be effected by the remote device in a similar manner to that with which the master unit may be operated by the remote device, as discussed above, The heater apparatus may further comprise an additional temperature sensor connected to the controller via the at least one communication port for determining the temperature of the external work piece. The external temperature sensor may he configured for measuring ambient air temperature.

the heater apparatus may further comprise a waterproof housing within which the source of heat, the at least one sensor, the controller, and the at least one conununication port are located, The heater apparatus may be 1P67 rated. ihe heater apparatus may include heat insulation. The housing may compnse aluminium.

Ihe heater apparatus may he arranged to operate in the power range SO to 500W although other values are contemplated. it may operate at 1 lOVac or 23OVac, although other values are contemplated. The source of heat may he arranged to operate at a maximum tcmperature of 80 degrees Centigrade although other temperatures arc contemplated. The temperature of the source of heat may be controllable to an accuracy of 0.8 degrees Centigrade. The apparatus may operate correctly in an ambient temperature range of-30 to 50 degrees Centigrade.

The heater apparatus may include at least two control loops mounted internally.

it may have a removable cover allowing access to a temperature adjustment means, such as provide by rotary sxvitches, User-programmable dip s\vitches may also he provided for varying the operation of' the apparatus. LED indicators may also be included providing a visual indication that the apparatus is operating and/or operating correctly.

Such TEDs may also be used tc, indicate the status of the po\ver supply and supervision (external control) status.

In a second aspect, the invention provides a heatet-system fot heating a phirality of external work pieces, the system comprising more than one heater apparatus according to the first aspect, and cornmunicahon means for each heater apparatus to communicate with the remote device.

S Ihe communication means may be one or more of fibre-optic or electrical cables, and wireless transmitters and receivers.

In a third aspect, the invention provides a method of controllably heating a work piece comprising the steps of providing a heater apparatus according to the first aspect, selecting an adapter block appropriately shaped fbr use with the work piece, attaching die adapter block to the apparatus, attaching die apparatus to die work piece, connecting the apparatus to an electrical supply, pre-setting the maximum temperature at which the heater shc,u]d operate, and switching on the apparatus.

Ihe apparatus may also be operable in a variety of control methods via user pre-selection at a programming stage using switches or other means. This may include single heating mode, dual mode (master/slave), test mode, adjustment of supervisory reporting and other such functions.

The method may further comprise the step of setting the ramp-rate at which the heater is to operate.

The invention offers an intelligent, electrical, compact, safe, all-in-one system with very effective heat flow rates for these complex work pieces Ihe key points of the invention include that the system is modular, intelligent, has high heat flow, provides important status information via a communication port and most importantly, does not exclusively require any external control system to frmnction correctly, since the whole conttol and heating system may exist in one module, unlike all alternative offerings for such heating applications. It therefbre requires a low skill level to install, and with some models no electrical skill. Being a bolt-on system, it is therefore fast to install and reniove.

The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example. the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference tigures quoted below refer to the attached drawings.

Figure 1 is a perspective view ot a heater apparatus from near one end; Figure 2 isa perspective view of the heater apparatus ot Figure 1. from near the opposite end; Figure 3 is a perspective exploded view of the heater apparatus of Figure 1; S Figure 4 is a perspective view of a pair of heater apparatuses placed on a work piece; Figure 5 to 10 are schematic views of various configurations of heater apparatuses.

Ihe present invention will be described with respect to certain drawings but the invention is nor limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. Each dr-awing may not include all of the features of the invention and therefore should not necessarily be considered to be an embodiment of the invention. In the drawings, the size of some of the elements may he exaggerated and not drawn to scale for illustrative purposes. The and the relative dimensions do not correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for disfinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatialh, in ranking or in any other manner. It is to he understood that the tenus so used are interchangeable under appropriate circumstances and that operation is capable in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative posifions. It is to be understood that the terms so used are interchangeable uuder appropriate circumstances and that operation is capable in other orientations than described or illustrated herein.

It is to be noticed that the term CCco1prisi1g used in the claims, should nor be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to he interpreted as specifying the presence of the stated features, integers, steps or components as referred to, hut does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope cif the expression cca device comprising means A and B'' shc,uld nc,t he limited tci devices consisting only of components A and B. It means that with respect to tile present invention, the only relevant components of the device are A and B. Siniilarly, it is to be noriced that the term "connected" used in the description, should not he interpreted as being restricted to direct connections only. Thus, the S scope of the expression "a device A con ected tc a device B" should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. it means that there exists a path between an output of A and an input of B which may be a path including other devices or means. "Connected" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other, Reference throughout this specification to an embodiment'' or an aspect" means that a particular feature, structure or characteristic described in connection with the embodiment or aspect is included in at least one embodiment or aspect of the present invention. thus, appearances of the phrases "in one embodiment", "in an embodiment", or "in an aspect" in various places throughout this specification are not necessarily all referring to the same embodiment or aspect, but may refer to different embodiments or aspects. F-'urthennore, die particular features, structures or characteristics of any embodiment or aspect of the invention may he combined in any suitable manner, as would he apparent to one of ordinary skill in the art from this disclosure, in one or niore embodiments or aspects.

Similarly, it should he appreciated that in the description various features of the invention are sometimes grouped togcther in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one cir more of the various inventive aspects. This method of disclcisure, hc,wever, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each clainm, Moreover, tire description of any individual drawing or aspect should not necessarily he considered to he an embodiment of the invention. Rather, as the following claims reflect, inventive aspects lie in fewer than all features of a single thregoing disclosed embodiment. i'hus, the claims thllowing the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some features included in other embodiments, combinations of features of different einbodhnents are meant to be \vithm the scope of the invention, and form yet further embodiments, as will be understood by those skilled in the art. Fc,r example, in the following claims, any S of the claimed embodiments can be used in anY combination.

In the description provided herein, numerous specific details are set forth.

However, it is understood that embodiments of the invention may he practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of

this description.

In the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of said values is more highly preferred than the other, is to he construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred valne and also to each value lying between said less preferred value and said intermediate value.

lie use of the tenn at least one" may mean only one in certain circumstances, The principles of the invention will now he described by a detailed description of at least one drawing relating to exemplary features of the invention, It is clear that other arrangements can be configured according to the knowledge of persons skilled in the art without departing from the underlying concept or technical teaching of the invention, the invention being limited only by the terms of the appended claims.

In Figure 1 a heater apparatus 10 is depicted. It comprises a housing 20 comprising an elongate substantially parallelepiped structure approximately 175mm long by 58mm wide by 55mm high. Larger scale heater apparatuses are possible which have approximate lengths of 200mm, 300mm, 400nim, 500nirn or longer.

The sidevalls of the housing curve inwardly at their upper ends creating an arch-like shape when viewed along the length of the housing.

Ihe housing 20 is closed at both ends, in Figure 1 one end wall 25 is shown, On this end wall two connector ports 30, 40 are shown, One of these connector ports is for connecting to a power supply and the other for connection to a communication means for remote monitoring and/or operation of the apparatus 10. These two connector ports may be replaced by single flexible conduits at each end.

Figure 2 depicts the apparatus 10 from near the opposite end of the one showia in Figure 1. The other end wall 26 is visible. This also comprises two connector ports 30, 60, One ot these conncctor pcrts 50 is fix connecting to another heater apparatus to supply power to it, and the other for connection to a remote sensor such as a temperature sensor.

An exploded view of the apparatus 10 is shown in Figure 3. The outer surface of one end wall 23 is shown together with the inner surface of the other end wall 26, The housing 20 is shown empty, the inside controller unit 70 having been removed. An access panel 21 is also shown above the housing 20. Its removal reveals a hole on the top wall of the housing 20 through which the control unit 70 is accessible. For instance.

rotary controller 72 arranged on the top of the control unit 70 are accessible.

On the lower surface of the control unit 70 a heater 74 inside a heat sink 75 is arranged together with a plate 77 thereunder for transfer of heat to the work piecc either directly, or indirectly via an adapter block (not shown).

In use a heater apparatus 10 may be placed on a work piece 110 as showii in Figure 4. An adapter block 120 is arranged between the apparatus 10 and the work piece 110. This adapter block 120 has a relatively flat upper surface fiji' contact with the lower surface of the plate 77 provided on the underside of the apparatus. It also has a curved lower surface for matching the curvature of the work piece, which in this case is a pipe 110. The adapter block 120 may be screwed to the base of the heater apparatus 10.

The adapter block 120 may have dimensions of 240mm long by 68mm wide with a depth of tip to 29mm.

Figure 4 also shows a second heater apparatus 10 placed on a work piece 110 with an adapter block 120. In use, the two heater apparatuses 10 may be connected together as will be described below.

Ihe two adapter blocks 120 may he held in position relative to the work piece 120 by means of straps (not shown) which extend around the work piece 120 and through channels 124 transversely provided at each end of the adapter blocks, Other ways of retaining the adapter blocks 120 to the work piece 110 are contemplated. For instance, the sides cif the adapter blocks 120 may include a series of ridges 122 running parallel to the length of the heater apparatus 10. Rods 130 may be attached to the work piece 110 or some other object to retain them in relation to the work piece 110. Ihe ridges 122 on the sides of the adapter blocks 120 may fit within the rods to substantially retain the apparatus in relation to the work piece 110. Each apparatus 10 may slide S along the length ot the rod 130 relative tc the work piece 110 to position the heater as required.

lEe adapter block 120 may he attached to the work piece 111 by means of magnets and the apparatus 10 may include such magnets.

In Figure 5 a first arrangement 200 is shown comprising a heater apparatus 10, including an adapter block 120, affixed to a work piece 110 with two straps 132, one at each end of the apparatus 10. Connecting means 205, such as cables, connect the heater apparatus, using the connection ports 30, 40, via a junction box 212 to a power supply via cable 213 and a supervisory system via cable 214. Ihe supervisory system may he a monitoring and/or control system. In use, the heater apparatus 10 heats the work piece 110, It may autonomously operate or he controlled remotely by the supervisory system.

In Figure 6, a second arrangement 300 is showii comprising a first "master unit" heater apparatus 10, including an adapter block 120, affixed to a work piece 110 with two straps 132, one at each end of the apparatus 10. A second "slave unit" heater apparatus 399 is also shown attached to the work piece 110. Although not shown, the slave unit apparatus 399 may also include an adapter block and attachment straps. lEe slave unit 399 is connected to the master unit, using the connection ports 50, 60, via a cable 206 and a junction box 216. Connecting means 205, such as cables, connect the master unit, using the connection ports 30, 40, via a junction box 212 to a power supply and a supervisory system. The supervisory system may be a monitoring and/or control system. In use, the master unit controls the slave unit and both may heat the work piece 110. Either or both may autonomously operate or be controlled remotely by the supervisory system.

The slave unit 399 may have a length in the range 110mm to 250mm, by 35mm wide and 35mm high, although different sizes, including larger dimensions, are contemplated.

Figure 7 shows a third arrangement 400 \vhich is sinlilar to the first arrangement shown in Figure 5. The difference lies in the fitct that a remote temperature sensor 418 is connected to the heater apparatus 10 via a cable 411. In this way the heater apparatus may rely on its own internal temperature sensor and/or the external remote temperature sensor to control its operation.

Figure 8 shows a fourth arrangement 500 which is similar to the second arrangement shown in Figure 6. The difference lies in the fact that a remote S temperature sensor 418 is connected to thc master unit 10 via a cable 411, In this way the master unit 10 may rely on the internal temperature sensors of itself and/or the slave unit, and/or the external remote remnperat-ure sensor to conftol irs operation and that of the slave unit.

Figure 9 shows a fifth arrangement 600 which is also sinular to the second arrangement shown in Figure 6. The difference lies in the fact that rather than die master and/or slave units being connected to the supervisory system via the junction lxix 212, it is/they are cc,nnected via a digital interface 630 and then a cable 614 to the supervisory system. the digital interface 630 may be connected to more than one heater apparatus thus acting as a node to locally-placed apparatus 10 with only a single connection from it to the supervisory system. This reduces the length of cable required compared to the situation where each heater apparatus 10 is connected separately to a supervisory system.

Finally hi Figure 10 a sixth arrangement 700 is shown comprising a junction box 710 (which could be a digital interface) connected to various combinations of heater apparatuses 10 and slave units 39 as will he explained.

1k first heater apparatus 101k, shown top left, has the san-ic operation capabilities as that described with reference to the first arrangement shown in Fiire 5.

Ihe second heater apparatus 1(113, shown middle left, has the san-ic operation capabilities as that described with reference to the second arrangenient shown in Figure 6. It is connected tc a slave unit 399k The third heater apparatus bC, shown bottom left, has the same operation capabilities as that described with reference to the fourth arrangement shown in Figure 8. It is connected Ic, a slave unit 399B and has a remote temperature sensor 418.

Ihe fourth heater apparatus 1OD, shown top right, also has the same operation capabilities as that described with reference to the second arrangement shown in Figure 6. It is connected to a slave unit 399C.

The fifth heater apparatus I OF. shown middle right, has a similar arrangement to that described with reference tci the second arrangement shown in Figure 6 except that there are two slave units 399D, 399F connected to the master unit I OF via a junction box 716. the master unit lOB may control each slave unit 399D, 399E individually or in conibination, Finally, the sixth heater apparatus lOP, shown bottom right, has he same S operation capabilities as that described with reference to the third arrangement shown in Figure 7. It is connected to a remote temperature sensor 418.

Ihe first and sixth arrangements have an independent control ioop, whereas the second to fifth arrangements each have a twin independent control loop such that each heater apparatus in each arrangement may be independenfly supervised and/or controlled.

\Vhere cables have been described herein it will be understood that communication may be by wireless means instead or, or as well as, by direct wire connections.

Claims

ClAIMS 1. A heater apparatus for attachment to an external work piece for heating thereof, the apparatus comprising a source of heat, at least one sensor, a controller fir S controlling the apparatus, at least one corninumcation port, attachment means tbr attaching an adapter block, and a replaceable pre-selected shaped adapter block attached to the apparatus via the attachment means, the shape selected for intimate contact with the external work piece, the adapter block for transferring heat from the source of heat to the external object by direct conduction.
2. The heater apparatus according to claim 1, wherein the sensor is a temperature sensor arranged within the apparatus.
3. The heater apparatus according to either one of claims 1 and 2, wherein die controller is arranged to control the ramp-rate of the source of heat.
4. the heater apparatus according to any preceding claim, wherein the controller is a microprocessor.
5. The heater apparatus according to any preceding claim, wherein the controller is attached to the source of heat.
6. The heater apparatus according to any preceding claim, wherein the controller is arranged to communicate, via the at least one communication port, actively and/or passively with a remote device so that the status of the apparatus may be determined from the remote device.
7. The heater apparatus according to any preceding claim, wherein die controller is arranged to communicate, via the at least one communication port, actively and/or passively with a remote device Sc) that the apparatus may he operated from the remote device,
8. The heater apparacus according to any preceding claim, wherein die controller is arranged to control at least one other heater apparatus via the at least cuic communication port.
9. The hearet-apparatus according to claim 8, wherein the controller is arranged to communicate, via the at least one conmiunication pot t, actively and/or passively with a remote device so that the status of the at least one other heatet apparatus may he determined from the remote device.
10. The heater apparatus according to either one of claims 8 and 9, wherein the controller is arranged to comniunicate, via the at least one communication port, actively and/or passively with a remote device so that the operation of the at least one other heater apparatus may be controlled from the remote device.
11. The heater apparatus according to any preceding claim, further comprising an additional temperature sensor connected to the controller via the at least one communication port for determining the temperature of the external work piece.
12. The heater apparatus according to any preceding claim, further comprising a waterproof housing within which the source of heat, the at least one sensor, the controller, and the at least one communicafion port are located.
13. A heater system for heating a plurality of external work pieces, the system comprising more than one heater apparatus according to any preceding claim.when directly or indirectly dependent on claim 6, and communication means for each heater apparatus to communicate with the remote device.
14. Ihe heater system of claim 12, wherein the conimunication means is one or more of fibre-optic or electrical cables, and wireless traisiitter* and receivers.
15. A method of controllably heating a work piece comprising the steps of providing a hearer apparatus according to any of claims 1 to 11, when directly or indirectly dependent on claim 6, selecting an adapter block appropriately shaped for use with the work piece, attaching the adapter block to the apparatus, attaching the apparatus to the work piece, connecting the apparatus te an electrical supply, pre-setting the maximum temperature at which the heater should operate, and switching on the apparatus.
16. The method of controllably heating an object according to claim 14, fnrther coinpnsing the step of setting the ramp-rate at which the heater is to operate.
17, A heater apparatus substantially as hereinbefore described with reference to the accompanying drawings.
18. A heater system substantially as hereinbefore described with reference to the accompanying drawings.